1. Field of the Invention
The invention relates to an electric power conversion system and, more particularly, to an electric power conversion system that exchanges electric power between a primary electric power conversion circuit and a secondary electric power conversion circuit.
2. Description of Related Art
There has been developed an electric power conversion system that exchanges electric power between a primary electric power conversion circuit and a secondary electric power conversion circuit magnetically coupled to the primary electric power conversion circuit.
As a related technique of the invention, for example, U.S. Pat. No. 7,408,794 describes an electric power conversion circuit that includes three input/output ports and half-bridge circuits. A high-voltage inverter circuit, a 14V load and a 42V load are respectively connected to the three input/output ports of the electric power conversion circuit.
Japanese Patent Application Publication No. 2006-187147 (JP 2006-187147 A) describes an electric power conversion circuit that includes two input/output ports and full-bridge circuits. The electric power conversion circuit includes three reactors in addition to reactors that constitute a transformer. There is also disclosed that a high-voltage inverter and a low-voltage electronic device are respectively connected to the two input/output ports of the electric power conversion circuit.
In the above electric power conversion system, a power transfer direction and a power transfer amount are controlled by equalizing the terminal voltage waveform of a primary coil of the primary electric power conversion circuit to the terminal voltage waveform of a secondary coil of the secondary electric power conversion circuit and then adjusting a phase difference φ between the two voltage waveforms. However, if the primary electric power conversion circuit and the secondary electric power conversion circuit are caused to operate in a state where an off time δ1 of the primary electric power conversion circuit and an off time δ2 of the secondary electric power conversion circuit are different from each other, the relationship between the terminal voltage waveform of the primary coil and the terminal voltage waveform of the secondary coil collapses. Therefore, there is a possibility that transfer of electric power between the primary electric power conversion circuit and the secondary electric power conversion circuit cannot be controlled by adjusting the phase difference φ.